Since a curable silicone composition forms a cured product that has excellent weather resistance, heat resistance, and similar properties and is rubber like (i.e. has hardness, elongation, or the like), curable silicone compositions are used as sealing agents, protective agents, or coating agents for semiconductor elements in optical semiconductor devices such as photocouplers, light emitting diodes, solid-state image sensing devices, or the like.
Various types of such curable silicone compositions have been proposed. For example, in Japanese Unexamined Patent Application Publication No. 2000-198930 an addition curing type silicone composition is proposed that comprises a diorganopolysiloxane having at least 2 alkenyl groups per molecule, an organopolysiloxane having a resin structure and having a vinyl group, an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, and a hydrosilylation reaction catalyst. Moreover, in Japanese Unexamined Patent Application Publication No. 2005-076003 an addition curing type silicone composition is proposed that comprises a linear organopolysiloxane having diphenylsiloxane units and having at least 1 alkenyl group per molecule, a branched organopolysiloxane having a vinyl group and a phenyl group, an organopolysiloxane having a diorganohydrogensiloxy group, and a hydrosilylation reaction catalyst. Moreover, in Japanese Unexamined Patent Application Publication No. 2007-327019 a curable organopolysiloxane composition is proposed that comprises an organopolysiloxane that has at least 2 alkenyl groups per molecule where at least 20 mol % of the total silicon-bonded organic groups are aryl groups; an organohydrogenpolysiloxane having silicon-bonded hydrogen atoms; an organopolysiloxane having per molecule at least 5 mol % of the total silicon-bonded organic groups as alkenyl groups, having at least 5 mol % of the total silicon-bonded organic groups as aryl groups, having at least 5 mol % of the total silicon-bonded organic groups as alkoxy groups, and having at least 5 mol % of the total silicon-bonded organic groups as epoxy-containing organic groups; and a hydrosilylation reaction catalyst. Further, in Japanese Unexamined Patent Application Publication No. 2008-001828 a curable organopolysiloxane composition is proposed that comprises an organopolysiloxane having per molecule at least 2 alkenyl groups and at least one aryl group, an organopolysiloxane having per molecule at least 0.5 mol % of total silicon-bonded organic groups as alkenyl groups and at least 25 mol % of total silicon-bonded organic groups as aryl groups, an organopolysiloxane having per molecule an average of at least two silicon-bonded aryl groups and an average of at least two silicon-bonded hydrogen atoms, and a hydrosilylation reaction catalyst.
However, when the curable silicon compositions proposed in the aforementioned patent documents are used as sealing resins for semiconductor elements, the cured product of the curable silicone composition has poor thermal shock resistance. Thus there have been problems such as the ready occurrence of cracks in the resin due to thermal shock, and particularly failures such as non-lighting when the aforementioned semiconductor element is a light emitting diode.
The objects of the present invention are to provide a curable silicone composition that forms a cured product having excellent transparency and thermal shock resistance, and by using this composition, to provide an optical semiconductor device that has excellent reliability.